Cast-in-situ bored pile construction method

Abstract

The invention relates to the technical field of cast-in-situ bored pile construction, in particular to a cast-in-situ bored pile construction method which comprises the following steps: S1, construction lofting; s2, burying a pile casing; s3, rotary digging and hole forming; s4, designing a slag removal soft drill bit, wherein the slag removal soft drill bit comprises a grouting pipe, a drill bit body installed at the bottom of the grouting pipe, a connector installed at the top of the grouting pipe and stirring teeth spirally installed on the outer wall of the grouting pipe, and the stirring teeth are steel wire ropes; s5, a slag removal soft drill bit is replaced on the main drill rod, and slag removal and hole cleaning are conducted for the first time; s6, lowering a reinforcement cage; and S7, a guide pipe is installed, and concrete is poured. In the first deslagging and hole cleaning process, the steel wire rope is used for stirring the teeth, grouting and hole sweeping are carried out at the same time, sediment floats and circulates out of a hole opening to be cleaned, the slag cleaning efficiency can be improved, the slag cleaning cost can be reduced, and meanwhile the influence on the soil quality in the slag cleaning process is reduced to improve the pile forming quality of a cast-in-place pile.

Description

Technical Field

[0001] The present application relates to the technical field of bored cast-in-place pile construction, and in particular to a bored cast-in-place pile construction method. Background Art

[0002] Cast-in-place piles are a common foundation engineering structure, widely used in construction, bridges, subways and other projects. It forms a pile body underground by drilling holes, and then reinforces the soil layer by pouring concrete to bear the load of the upper structure. It is suitable for various soil conditions, especially for foundation construction in soft soil or uneven soil.

[0003] Underground engineering is regional and hidden. In the process of bored pile drilling, drill bit falling off due to reasons such as hole collapse, cage jam, excessive sediment, continuous operation of machinery or irregular construction often occurs. At present, the repeatable high-pressure grouting technology is generally used, that is, the pile end post-grouting process and the sediment washing and treatment sediment at the bottom of the pile are used. The slag removal efficiency of this technology is low and the cost is high. In addition, when using high-pressure grouting to remove slag, due to the high grouting pressure, the soil around the pile hole may be pressed out or loosened, thereby reducing the bonding force between the pile foundation and the soil; or the high-pressure flow of high-pressure grouting may cause disturbance of the surrounding soil, especially in soft soil or loose soil layers. High-pressure grouting may cause the loss or displacement of the soil around the pile hole. Therefore, after the pile is formed, it is easy to cause soil loss and water seepage between piles, affecting the quality of the bored pile. Therefore, further improvements can be made. Summary of the invention

[0004] In order to improve the slag removal efficiency and reduce the slag removal cost in bored cast-in-place pile construction, and at the same time reduce the impact on soil quality during the slag removal process to improve the quality of bored cast-in-place piles, the present application provides a bored cast-in-place pile construction method.

[0005] The present application provides a bored pile construction method using the following technical solution: A bored pile construction method comprises the following steps: S1, construction layout; S2, burying casing; S3, rotary drilling to form a hole; S4, design of a slag cleaning soft drill bit: the slag cleaning soft drill bit comprises a grouting pipe, a drill bit installed at the bottom of the grouting pipe, a joint installed at the top of the grouting pipe and stirring teeth installed on the outer wall of the grouting pipe in a spiral arrangement, and the stirring teeth are a rope structure with certain flexibility; S5, replacing the slag cleaning soft drill bit on the main drill rod to perform the first slag removal and hole cleaning; S6, lowering a steel cage; S7, installing a guide tube and pouring concrete.

[0006] By adopting the above technical solution, during the construction process, after the hole is drilled, the slag-clearing soft drill bit is replaced on the main drill rod to remove slag and clean the hole. Under the action of the grouting pipe and stirring teeth of the slag-clearing soft drill bit, the hole is swept while grouting, so that the sediment floats and circulates out of the hole. At the same time, the buried objects such as sediment in the hole can be cleaned, which is convenient for salvaging the fallen objects. It can efficiently handle the sediment at the bottom of the pile, improve the slag-clearing efficiency and reduce the slag-clearing cost in the construction of bored piles, and reduce the impact on the soil quality during the slag-clearing process to improve the pile quality of the bored pile. It has the characteristics of convenient operation, safety and reliability, and low preparation and use costs.

[0007] Optionally, the stirring teeth are relatively soft steel wire ropes with certain rigidity.

[0008] By adopting the above technical scheme, since the steel wire rope has a certain rigidity and is relatively soft, on the one hand, the flexibility of the steel wire rope can produce deformation. During the slag cleaning process, it can perform contact cleaning through a certain degree of deformation, and at the same time can avoid jamming due to slag cleaning collision to ensure the smooth progress of slag cleaning; on the other hand, the rigidity of the steel wire rope enables it to maintain a strong cleaning force, so that it can better clean and stir the drill cuttings, and its hole sweeping and slag cleaning effect is better.

[0009] Optionally, during the process of lowering the steel cage in step S6, a slag-clearing soft drill bit is used to clean the hole, effectively removing attachments on the steel cage without damaging the steel cage, and drilling to the bottom of the hole allows the sediment to float up and be led to the slurry outlet, so as to assist the smooth lowering of the steel cage.

[0010] By adopting the above technical solution, the steel cage is stuck due to the disturbance of the steel cage being lowered and the long hole-stopping time, and the hole wall collapses and buries the steel cage. In this process, the flexible stirring teeth in the slag-clearing soft drill bit are used to sweep the hole, effectively removing the attachments on the steel cage without damaging the steel cage, and drilling to the bottom of the hole to make the sediment float up and lead to the slurry outlet to assist the smooth lowering of the steel cage. It can handle the situation of ultra-deep engineering pile stepping holes, cage jams, etc., save time for lowering the steel cage and pouring concrete, and reduce engineering risks.

[0011] Optionally, in step S7, after the catheter is installed in place, a matching cover is installed on the catheter, and mud with a specific gravity of 1.2-1.3 is pumped to the bottom of the hole with a large pump volume to replace the drill cuttings that have settled when the steel cage and the catheter are lowered and the mud with higher density that still suspends the drill cuttings at the bottom of the hole for secondary hole cleaning.

[0012] By adopting the above technical scheme, the secondary hole cleaning treatment is carried out to replace the drill cuttings that have settled when the steel cage and the guide tube are lowered and the denser mud with the drill cuttings still suspended at the bottom of the hole, so as to clean the drill cuttings in the borehole again to ensure the molding quality of the bored piles formed after the subsequent concrete pouring.

[0013] Optionally, after step S3, a hole drilling inspection is performed: including testing various technical indicators of the pile hole. If the test is qualified, the next process is carried out; if it is unqualified, the process returns to the rotary drilling process for processing.

[0014] Optionally, step S1 includes: making points on the extension line of the axis according to the leveling points, measurement control network and pile layout provided by the survey unit, locating the coordinate piles using a total station, and locating them with wooden stakes and steel nails; placing reference piles according to the coordinate piles using a theodolite and a steel ruler, setting one every ten piles, placing the reference piles with wooden stakes and steel nails, and marking the pile numbers on the reference piles, locating the remaining piles with steel bars or bamboo chopsticks, and marking them with white lime, and using reference stakes to verify adjacent pile positions during construction; laying out the outer wall edge lines of the main structure to check whether the pile positions meet the requirements, and after the laying out is completed, it needs to be verified and re-inspected, and reported to the supervisor for acceptance.

[0015] By adopting the above technical solution, during the construction layout process, on the one hand, adjacent pile positions are checked with reference piles, and on the other hand, pile positions are corrected using the edge lines of the main structure's outer wall, which can prevent pile position deviations and further ensure construction quality.

[0016] Optionally, step S2 includes: positioning the casing, first aligning the center of the casing with the steel bar cross fork, and then pulling up the pile protection cross line to make the two cross centers coincide. If it exceeds the deviation range, it can be adjusted until it is qualified; hoisting the lower casing, aligning the center of the casing with the pile position, and the verticality of the casing can be adjusted by a plumb bob or a level ruler, and the casing is lowered vertically, and the top of the casing is not less than 10 cm above the ground after lowering; after the casing is lowered, the area around the casing is backfilled and compacted with clay, and the casing is firmly fixed on the pile or wooden board.

[0017] By adopting the above technical solution, during the process of burying the casing, the casing is centered and regulated by aligning the center of the steel bar cross fork with the cross line of the pile, so as to ensure the verticality of the casing during the pre-embedding process, thereby ensuring the construction quality of subsequent drilling and pouring. In addition, after the casing is lowered, it can be prevented from falling into the bottom of the pile hole due to accidental operation by further fixing the casing on the pile or the wooden square.

[0018] Optionally, during the first slag removal and hole cleaning process in step S5: at the beginning of hole cleaning, replace and lower the slag cleaning soft drill bit, lift the slag cleaning soft drill bit 0.2-0.3m away from the bottom of the hole, keep the drill bit rotating slowly at low pressure while inputting circulating mud; during drilling, reasonably adjust the drilling speed according to different geological conditions, not exceeding 10m / h at the fastest, strictly control the mud quality, and inject mud into the hole in time to make the mud water level in the hole 1m higher than the groundwater level.

[0019] Optionally, in step S7, during the concrete pouring process: the concrete slump is 200-220 mm, and each time a tube of concrete is injected, the tube is pulled upward by a crane, and each time it is lifted 0.2-0.4 m, half of it is inserted back, and this cycle is repeated until the top surface.

[0020] By adopting the above technical solution, during the process of pouring concrete, the conduit is pulled upwards by half every time it is lifted by 0.2-0.4m, which can ensure the diffusion and compaction of the concrete.

[0021] In summary, the present application includes at least one of the following beneficial technical effects: 1. During the construction process, after the hole is drilled, replace the slag-clearing soft drill bit on the main drill rod to remove slag and clean the hole. Under the action of the grouting pipe and stirring teeth of the slag-clearing soft drill bit, the hole is swept while grouting, so that the sediment floats and circulates out of the hole. At the same time, it can clean up the buried objects such as sediment in the hole, which is convenient for salvaging the fallen objects. It can efficiently handle the sediment at the bottom of the pile, improve the slag-clearing efficiency and reduce the slag-clearing cost in the construction of bored piles, and reduce the impact on the soil quality during the slag-clearing process to improve the pile quality of the bored pile. It has the characteristics of convenient operation, safety and reliability, and low preparation and use costs. 2. Since the steel wire rope has a certain rigidity and is relatively soft, on the one hand, the flexibility of the steel wire rope can produce deformation. During the slag cleaning process, it can be deformed to a certain extent to perform contact cleaning, and at the same time, it can avoid the jamming state caused by the collision of slag cleaning, so as to ensure the smooth progress of slag cleaning; on the other hand, the rigidity of the steel wire rope enables it to maintain a strong cleaning force, so that it can better clean and stir the drill slag, and its hole cleaning and slag cleaning effect is better; 3. When lowering the steel cage, the hole wall collapses and buries the steel cage due to the disturbance caused by lowering the steel cage and the long hole-stopping time, causing the steel cage to get stuck. In this process, the flexible stirring teeth in the slag-clearing soft drill bit are used to sweep the hole, effectively removing the attachments on the steel cage without damaging the steel cage, and drilling to the bottom of the hole to float the sediment to the slurry outlet to assist the smooth lowering of the steel cage. It can handle situations such as pile stepping holes and cage jams in ultra-deep projects, save time for lowering the steel cage and pouring concrete, and reduce engineering risks; 4. Through the secondary hole cleaning treatment, the drilling debris that has settled at the bottom of the hole due to the lowering of the steel cage and the guide tube and the high-density mud with suspended drilling debris can be replaced, and the drilling debris in the borehole can be cleaned again to ensure the molding quality of the bored piles formed after the subsequent concrete pouring. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The invention discloses a construction flow chart of a bored cast-in-place pile construction method.

[0023] Figure 2 It is the front view of the structural schematic diagram of the slag cleaning soft drill bit in this application.

[0024] Figure 3 It is a top view of the structural schematic diagram of the slag cleaning soft drill bit in this application.

[0025] Figure 4 This is a schematic diagram to show the specific installation method of the stirring teeth of the slag cleaning soft drill bit in this application.

[0026] Description of reference numerals: 1. Grouting pipe; 2. Drill bit; 3. Joint; 4. Stirring teeth; 5. Fixed core pipe; 6. Tightening bolts. DETAILED DESCRIPTION

[0027] The following is combined with Figure 1-4 This application is described in further detail.

[0028] The embodiment of the present application discloses a bored cast-in-place pile construction method.

[0029] Reference Figure 1 A bored pile construction method comprises the following steps: S1. Construction layout: Including: according to the leveling points provided by the survey unit, the survey control network, and the pile position layout diagram, make points on the extension line of the axis, use the total station to locate the coordinate pile position, and use wooden stakes and steel nails to locate; According to the coordinate piles, the reference piles are placed with theodolite and steel ruler, one for every ten piles. The reference piles are placed with wooden stakes and steel nails, and the pile position numbers are marked on the reference piles. The remaining piles are positioned with steel bars or bamboo chopsticks and marked with white lime. During construction, the reference piles are used to check the adjacent pile positions. Lay out the edge line of the main structure's outer wall to check whether the pile position meets the requirements. After the line is laid out, it needs to be verified and re-inspected and reported to the supervisor for acceptance.

[0030] S2. Buried casing: Including: casing positioning, first align the center of the casing with the steel bar cross fork, then pull the cross line of the pile guard to make the two cross centers coincide. If it exceeds the deviation range, it can be adjusted until it is qualified; Hoist the lower casing, align the center of the casing with the pile position, and use the plumb bob or level to adjust the verticality of the casing. Lower the casing vertically, and the top of the casing should be no less than 10cm above the ground after lowering. After the casing is placed, backfill and compact the area around it with clay, and then firmly fix the casing on the pile or wooden plank.

[0031] S3, rotary digging into holes; The alternate hole construction method is adopted. After the drilling rig is installed in place, it is locked using its own locking function, and the center of the drill bit 2 is aligned with the center of the pile position to perform rotary drilling.

[0032] After the hole is completed, the hole inspection is carried out: including the inspection of various technical indicators of the pile hole. The hole quality should meet the design requirements. After passing the inspection, the next process will be carried out. If it fails, it will return to the rotary drilling process for processing.

[0033] S4, slag cleaning soft drill bit design: The slag cleaning soft drill bit includes a grouting pipe 1, a drill bit 2, a joint 3 and a stirring tooth 4, wherein the drill bit 2 is installed at the bottom of the grouting pipe 1 for assisting drilling. The joint 3 is installed at the top of the grouting pipe 1 for connecting with the main drill rod when replacing. The stirring tooth 4 is spirally arranged and installed on the outer wall of the grouting pipe 1. The stirring tooth 4 is a rope structure with a certain flexibility, and its length can be determined according to actual conditions.

[0034] In this embodiment, the grouting pipe 1 is a steel pipe with a length of 1200 mm and a wall thickness of ≥10 mm, which is convenient for injecting mud during drilling. The stirring teeth 4 are steel wire ropes, which have a certain rigidity and are relatively soft, and their length is greater than the diameter of the casing. The cross section of the drill bit 2 is a triangular structure, and a U-shaped groove is provided at the upper end of the drill bit 2. The outer periphery of the lower end of the grouting pipe 1 is fixedly connected to the U-shaped groove, and it is necessary to ensure that the thickness of the drill bit 2 is less than the inner diameter of the grouting pipe 1 during implementation. The drill tip of the drill bit 2 is inlaid with an alloy cutter head, which is convenient for drilling and avoiding hard objects.

[0035] In this embodiment, the stirring teeth 4 are fixedly installed by the fixed core tube 5. Among them, the grouting pipe 1 is spirally drilled with multiple through holes along the pipe wall, and the fixed core tube 5 is sleeved on the middle part of the cutting stirring teeth 4 and fixed with the cutting stirring teeth 4, and after being fixed, it penetrates into the through hole on the grouting pipe 1. Both ends of the fixed core tube 5 are provided with contraction grooves, so that both ends form two semicircular tubes with gaps. Threads are provided in the through hole, and the grouting pipe 1 is threadedly installed with fastening bolts 6 at both ends of the through hole. The middle part of the fastening bolt 6 is provided with a through hole, which is in a cone shape. The two ends of the fixed core tube 5 extend and penetrate into the through holes of the fastening bolts 6 at both ends. As the fastening bolts 6 are continuously screwed in, the two ends of the fixed core tube 5 are continuously tightened until the two fastening bolts 6 fix the two ends of the fixed core tube 5, thereby fixing the stirring teeth 4 and realizing the detachable fixed installation of the stirring teeth 4.

[0036] In other embodiments, the fixed core tube 5 is a round tube, which is mounted on the stirring teeth 4 and fixed to the stirring teeth 4 by welding. Then, after the fixed core tube 5 is inserted into the through hole on the grouting pipe 1, it is welded and fixed to the grouting pipe 1 to achieve the fixing of the stirring teeth 4 to the grouting pipe 1.

[0037] S5, first slag removal and hole cleaning: At the beginning of hole cleaning, replace and lower the slag cleaning soft drill bit, lift the slag cleaning soft drill bit 0.2-0.3m away from the bottom of the hole, keep the drill bit rotating slowly at low pressure while inputting circulating mud; during drilling, reasonably adjust the drilling speed according to different geological conditions, and the fastest speed shall not exceed 10m / h. Strictly control the mud quality, and inject mud into the hole in time to make the mud water level in the hole 1m higher than the groundwater level.

[0038] S6, lower the steel cage; Before lowering, make the steel cage first: the steel cage is made by the stiffening hoop forming method to ensure the position and angle of the steel bars are accurate. The reinforcement hoop is welded to the main reinforcement, and the spiral hoop is firmly tied to the main reinforcement. If there are 3 joints in the main reinforcement of the steel cage, lap welding is preferred. The welding length is not less than 10d for single-sided welding and not less than 5d for double-sided welding. The number of joints 3 of the main reinforcement on the same section shall not exceed 50% of the total number of main reinforcements. The reinforcement is connected to the main reinforcement by spot welding and is firmly connected to each vertical force-bearing main reinforcement; the stirrups are fixed to the main reinforcement by wire tying, and no missing or skipping is allowed. There should be horizontal sections at the beginning and end of the spiral stirrups, and the length should not be less than one and a half circles of the pile body diameter. The overlap of the spiral stirrups should be ≥Lae(39d), and a 135º hook should be made at the end. The straight section of the hook should take the larger value of 10 d and 75mm.

[0039] After the production is completed, it is lowered. At the same time, during the process of lowering the steel cage, a slag-clearing soft drill bit is used to clean the hole, which can effectively remove the attachments on the steel cage without damaging the steel cage. The bottom of the hole is drilled to make the sediment float up and lead to the slurry outlet, so as to assist the smooth lowering of the steel cage.

[0040] S7. Install the conduit and pour concrete: Before using the conduit, it should be tested for water tightness and can only be put into use after passing the test. The conduit is placed in by a crane. The diameter and length of the conduit should match the hole depth, and the distance between the conduit and the bottom of the hole should be 0.3m.

[0041] After the guide tube is installed in place, a matching cap is installed on the guide tube, and mud with a specific gravity of 1.2-1.3 is pumped to the bottom of the hole with a large pump volume to replace the drilling debris precipitated at the bottom of the hole due to the installation of the steel cage and the guide tube and the mud with a high density of drilling debris still suspended, so as to perform secondary hole cleaning, so as to clean the drilling debris in the borehole again to ensure the molding quality of the cast-in-place pile formed after the subsequent concrete pouring. Preferably, the specific gravity of the mud pumped to the bottom of the hole is 1.15.

[0042] After the secondary hole cleaning is completed, concrete is poured, wherein the concrete slump is 200-220mm, and each time a tube of concrete is injected, the tube is pulled upward by a crane, and half of it is inserted back every 0.2-0.4m, and this cycle is repeated until the top surface. Preferably, half of it is inserted back every 0.3m.

[0043] At the same time, after the concrete pouring is completed, the casing should be carefully pulled out in time by crane or excavator to ensure the quality of the concrete on the pile top.

[0044] In this embodiment, corresponding experimental tests need to be carried out at each construction stage, including: (1) The raw steel bars delivered to the site should be inspected for appearance and mechanical properties in accordance with the design requirements; (2) Steel bar mechanical and welding connection test pieces must be cut on site, and backstage production is strictly prohibited; (3) After the concrete arrives at the construction site, the slump should be checked. The designed slump is 180~220mm. The allowable deviation between the actual concrete slump and the required concrete slump is ±20mm. After the concrete arrives at the site and during the intervals of concrete pumping, the tank truck should be kept rotating at a constant speed. It is strictly forbidden to add water to the concrete tank truck under any circumstances. (4) During the construction of cast-in-place piles, each grouting shift shall produce at least one group of test blocks, with three test blocks retained in each group. The specifications are 150×150×150mm, standard curing, and the strength is tested after 28 days. (5) After the construction of supporting piles is completed, the integrity of the pile body shall be tested by low-strain dynamic testing. The number of tested piles should not be less than 20% of the total number of piles, and shall not be less than 5. When the integrity of the pile body is Class III or Class IV, the core drilling method shall be used for verification, and the number of low-strain dynamic testing shall be increased.

[0045] The implementation principle is: after the hole is formed by rotation, the slag-clearing soft drill bit is replaced on the main drill rod to carry out the first slag removal and hole cleaning. Under the action of the grouting pipe 1 and the wire rope stirring teeth 4 in the slag-clearing soft drill bit, the hole is swept while grouting, so that the sediment floats and circulates out of the hole mouth, and at the same time, the buried objects such as sediment in the hole can be cleaned, which is convenient for salvaging the fallen objects, can improve the slag-clearing efficiency and reduce its slag-clearing cost, and at the same time reduce the impact on the soil quality during the slag-clearing process to improve the pile quality of the cast-in-place pile.

[0046] The above are all preferred embodiments of the present application, and the protection scope of the present application is not limited thereto. Therefore, any equivalent changes made according to the structure, shape, and principle of the present application should be included in the protection scope of the present application.

Claims

1. A bored pile construction method, characterized in that: The steps include: S1. Construction layout; S2, burying casing; S3, rotary digging into holes; S4. Design of a slag-clearing soft drill bit: the slag-clearing soft drill bit comprises a grouting pipe (1), a drill bit (2) installed at the bottom of the grouting pipe (1), a joint (3) installed at the top of the grouting pipe (1), and a stirring tooth (4) installed on the outer wall of the grouting pipe (1) in a spiral arrangement, and the stirring tooth (4) is a rope structure with a certain flexibility; S5. Replace the slag-clearing soft drill bit on the main drill pipe to perform the first slag-clearing and hole-clearing; S6, lower the steel cage; S7. Install the conduit and pour concrete.

2. A bored pile construction method according to claim 1, characterized in that: The stirring teeth (4) are relatively soft steel wire ropes with certain rigidity.

3. A bored pile construction method according to claim 1, characterized in that: In the process of lowering the steel cage in step S6, a slag-clearing soft drill bit is used to clean the hole, effectively removing the attachments on the steel cage without damaging the steel cage, and drilling to the bottom of the hole allows the sediment to float up and be led to the slurry outlet to assist the smooth lowering of the steel cage.

4. A bored pile construction method according to claim 1, characterized in that: In step S7, after the guide tube is installed in place, a matching cover is installed on the guide tube, and mud with a specific gravity of 1.2-1.3 is pumped to the bottom of the hole with a large pump volume to replace the drilling cuttings precipitated when the steel cage and the guide tube are lowered and the mud with a higher density of drilling cuttings still suspended in the bottom of the hole for secondary hole cleaning.

5. A bored pile construction method according to claim 1, characterized in that: After step S3, the hole forming inspection is carried out: including testing various technical indicators of the pile hole. If the test is qualified, the next process is carried out. If it is unqualified, it returns to the rotary drilling process for processing.

6. A bored pile construction method according to claim 1, characterized in that: In step S1, it includes: According to the leveling points, survey control network and pile position layout provided by the survey unit, points are made on the extension line of the axis, the coordinate pile positions are located using the total station, and the positions are located using wooden stakes and steel nails; According to the coordinate piles, the reference piles are placed with theodolite and steel ruler, one for every ten piles. The reference piles are placed with wooden stakes and steel nails, and the pile position numbers are marked on the reference piles. The remaining piles are positioned with steel bars or bamboo chopsticks and marked with white lime. During construction, the reference piles are used to check the adjacent pile positions. Lay out the edge line of the main structure's outer wall to check whether the pile position meets the requirements. After the line is laid out, it needs to be verified and re-inspected and reported to the supervisor for acceptance.

7. A bored pile construction method according to claim 1, characterized in that: In step S2, it includes: To position the casing, first align the center of the casing with the steel bar cross, then pull the cross line of the pile guard to make the centers of the two crosses coincide. If the deviation is beyond the range, it can be adjusted until it is qualified. Hoist the lower casing, align the center of the casing with the pile position, and use the plumb bob or level to adjust the verticality of the casing. Lower the casing vertically, and the top of the casing should be no less than 10cm above the ground after lowering. After the casing is placed, backfill and compact the area around it with clay, and then firmly fix the casing on the pile or wooden plank.

8. A bored pile construction method according to claim 1, characterized in that: In the first slag removal and hole cleaning process in step S5: at the beginning of hole cleaning, replace and lower the slag cleaning soft drill bit, lift the slag cleaning soft drill bit 0.2-0.3m away from the bottom of the hole, keep the drill bit rotating slowly at low pressure while inputting circulating mud; during drilling, reasonably adjust the drilling speed according to different geological conditions, the fastest speed shall not exceed 10m / h, strictly control the mud quality, and inject mud into the hole in time to make the mud water level in the hole higher than the groundwater level by 1m.

9. A bored pile construction method according to claim 1, characterized in that: In step S7, during the concrete pouring process: the concrete slump is 200-220 mm, and each time a tube of concrete is injected, the tube is pulled upward by a crane, and each time it is lifted 0.2-0.4 m, half of it is inserted back, and this cycle is repeated until the top surface.

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